Over the past several years, the development of electronic devices such as laptop computers, hand held computers, personal data assistants (PDA) and global telephones has resulted in an increased demand for smaller semiconductor integrated circuits (IC) and other associated electronic components. In order to meet this demand, manufactures have developed several techniques to reduce the overall size and dimensions of an electrical component. Specifically, some of these techniques are aimed at circuit geometries that include smaller and more dense electrical components.
The manufacturing of complex semiconductor devices typically involves a series of processing steps, including deposition, photolithography and etching. During the photolithography process, semiconductor manufacturers use a photomask or a reticle to copy an image of an electronic circuit onto a semiconductor wafer. Photomasks generally include a transparent substrate that has a patterned opaque layer deposited on one surface. The patterned opaque layer typically includes multiple features that form a microscopic image of the electronic circuit.
As design rules have moved toward smaller and denser IC devices, the integrity of geometry on the photomask has become increasingly important. One key cause of degradation of the patterned layer on the photomask is electrostatic discharge (ESD). ESD is created when a force causes a charge imbalance among the features in the patterned layer of the photomask. For example, the substrate may become statically charged during handling. The static may attract contaminants, such as dust and other particles, to the photomask and degrade the microscopic image projected on to the semiconductor wafer. ESD may result when the opposite charge between features reaches a threshold, and the charge is passed between the features. This exchange of charge between features may cause damage to the photomask. In the case of very small patterns on the photomask, the damage may be severe enough to melt and/or blast the features in the patterned layer. The damage to the photomask may result in wafer scrap, rework, photomask repair, and considerable engineering and manufacturing time spent on in-line inspections and defect analysis.